Natural killer ((NK) cells are believed to play an important role in human tumor and viral defense mechanisms, as well as in immune regulation. NK cells cause the lysis of a wide range of target cells, but the mechanisms by which this lysis occurs are unresolved. Thus, the long term objectives of this study are to define at the cellular and, ultimately, the molecular level the events which occur in a tumor target cell which lead to its lysis after its lethal interaction with a human NK lymphocyte. We wish to understand how the various cellular processes are affected when these cells become "programmed" to lyse by NK lymphocytes. We have established in our laboratory the techniques necessary for the rapid isolation of pure "programmed" target cells after interaction with highly active NK cells. We have also discovered several probes capable of blocking the progression of the lethal hit in these "programmed" target cells. We will exploit this methodology to disclose further the sequence of events occurring in these cells which lead to their lysis. Our immediate goal is to reveal more information about these target cell isolated events. Because reduced temperature blocks completion of the lethal hit, we plan to investigate the role of several temperature-sensitive components of the target cell necessary for completion of the lethal hit. Specifically, we will investigate the role of target membrane movement, temperature-sensitive target enzymes, as well as active target cell processes such as protein synthesis. Finally, since trypsinization of programmed target cells blocks completion of the lethal hit, the biochemical characteristics of surface structures requisite for their lysis will be investigated. The complement-mediated lethal hit is understood in some detail at the molecular level. In view of the proposed biological and clinical significance of in vivo NK cell-mediated cytotoxic events, it is essential that a similar level of understanding be attained regarding the NK-generated lethal hit. The studies outlined in this research are vital initial steps to this goal. (SR)